Electric arc furnace with iron core choke means on electrode supply conductors



3,414,656 S ON Dec. 3, 1968 H. K. LUNIG ELECTRIC ARC FURNACE WITH IRON com: cuoxm MEAN ELECTRODE SUPPLY CONDUCTORS Filed Oct. 22, 1965 United States Patent 0 F 3,414,656 ELECTRIC ARC FURNACE WITH IRON CORE CHOKE MEANS 0N ELECTRODE SUPPLY CONDUCTORS Hermann Karl Liinig, Duisburg, Germany, assignor to Demag Elektrometallurgie G.m.b.H.-, Duisburg, Germany Filed Oct. 22, 1965, Ser. No. 501,751 Claims priority, application Germany, Jan. 28, 1965, D 46,377 8 Claims. (Cl. 139) ABSTRACT OF THE DISCLOSURE An electric arc furnace has movable electrodes and current conductors connecting the electrodes to a source of current and each including a flexible portion. Individual and separate choke elements, in the form of annular iron cores, are placed around at least the flexible portions of the conductors to adjust the inductances to equalize the currents. The choke elements may replace a corresponding number of individual insulating elements surrounding the flexible portions of the conductors.

Background of the invention This invention relates in general to the construction and operation of electric furnaces and in particular to a new and useful electric furnace installation with flexible current leads having choke coils which are formed as a plurality of relatively small size choke elements which are arranged, in a number set by experience of operation of the furnace, preferably along the flexible connecting line.

The invention has application to are and similar type electrical furnaces, single phase as well as multi-phase. The invention has particular application to three-phase arc furnaces with flexible leads connected to the electrodes which, in turn, are secured on a rigid holder movable in relation to the furnace tank. It is known that different currents may occur between the various phases or the various conductors assigned to these phases and also different currents may occur in conductors assigned to each phase, that is, for example, in single phase furnaces different currents may occur. In order to eliminate such current differences, choke arrangements have been used. An attempt has been made to equalize, at least in part,

the differences between the phases by arranging on the current bus bars behind the transformer one or more choke coils. These choke coils are provided for bringing the current in the individual phases to an identical value insofar as is possible. Another type of construction is permanently applied on the suspension cable for ensuring that the currents in the conductors of the individual phases are brought to identical values. The choke coils must be so designed that they fulfill either the one function, that is, the equalization between the phases, or the other function, namely the equalization between the conductors of the same phase.

For known reasons the current differences to be expected cannot, however, be exactly determined from the outset.

This is so because, among other reasons, three-dimensional magnetic fields of this kind can no longer be exactly expressed mathematically. For this reason the proposed aim can easily be obtained only partly.

It has been customary to take precautions against overheating of the conductors by applying, at spaced locations, insulators of a material such as wood, for example, so that all of the conductors of one phase may assume circular or rectangular form. In addition, insulating elements are employed surrounding the cables.

3,414,656 Patented Dec. 3, 1968 In accordance with the invention it is possible to make an empirical adaptation of the system to the conditions which would prevail in a furnace. In addition, with the invention it is possible to establish choking in a particularly simple and inexpensive manner and in the same manner for all furnaces.

In accordance with the invention there is provided a choke arrangement which comprises a plurality of individual choke elements of a construction such that they may surround a single flexible or fixed conductor and may be arranged one after the other. The choke elements are advantageously constructed such that they may be fixed in position or may be movable. In a preferred arrangement the weight of the choke elements may be supported directly on the cable with which they are employed. In some instances, however, it is desirable to provide separate suspension for the choke elements which will entirely or partly absorb their weight. It is of particular advantage in accordance with one concept of the invention to string the elements one behind the other on the cable in the manner of a string of beads, the external design of the choke elements being similar to that of a link type insulating section which may also be employed.

The invention makes it possible to effectively control both the phase differences and the differences in the transmitted current strength of the individual conductors of one phase. On the other hand, the invention also makes it possible to select a desired asymmetry between the individual phases so that according to the existing thermal conditions in the furnace a uniform wear of the refractory masonry becomes possible.

In accordance with the method of the invention, in order to operate the furnace first a number of elements to be used according to a rough calculation are employed by stringing them along a conductor. If it is then found during operation that undesired current differences exist or that individual conductors heat up too much then the desired state may be established by the simple addition or elimination of choke elements. In this manner it is possible to establish extensive uniformity of current distribution in the individual phases and in the individual conductors. Even if in the course of the operation any changes occur which bring about subsequent differences, the adaptation is particularly simple since it involves only the removal or addition of the individual choke elements to convert the installation as required.

A particularly preferred embodiment is the construction of choke elements in the same manner as insulating elements so that an exchange of these two elements is possible. The choke elements may be closed ring cores, or they may be designed so they do not form closed cores but are in two or more parts so that it is possible to clamp the two parts around the conductor or detach them therefrom. The choke elements may be provided with spacer means in order to ensure that the individual conductors are maintained at suitable distances from each other. Each of the choke elements advantageously includes a ring core which may consist, for example, of wound layers of dynamo sheet or of stamped ring sheets or of ferromagnetic baked cores of low heat loss. The core is inter rupted in one or more places so that two or more shells are formed which are held together, for example, by simple bolts or other securing or clamping means.

Accordingly, it is an object of the invention to provide an improved method of operating a furnace using choking elements.

A further object of the invention is to provide an electric furnace construction having choking elements which comprise a plurality of relatively small size individual cellar members which are adapted to be fitted over the conductors.

A further object of the invention is to provide a choking element for application to the electrical conductors of a furnace which are advantageously in the form similar to the usual insulation elements and which may be strung or positioned in relation to the conductors in a simple and easy manner.

Another object of the invention is to provide means for connection to the electrical conductors of an electric furnace which are simple in design, rugged in construction and economical to manufacture.

The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating ad vantages and specific objects attained by its use, reference should be had to the accompanying drawings in which there are illustrated and described preferred embodiments of the invention.

In the drawings:

FIG. 1 is a somewhat schematic elevational and partial sectional view of an electrical furnace system having choking elements constructed in accordance with the invention;

FIG. 2 is a front elevational view of an uncooled choke element constructed in accordance with the invention;

FIG. 3 is a section taken on the line 3-3 of FIG. 2;

FIG. 4 is a view similar to FIG. 3 of another embodiment of choke element; and

FIG. 5 is a section taken on the line 5--5 of FIG. 4.

Referring to the drawings in particular, the invention as embodied in FIG. 1 is incorporated on an electric furnace having a transformer 1 which is connected to a bus bar 2. Flexible leads or cables 3 extend from the bus bar 2 to a bus connection or electrode holder 6 which holds the furnace electrodes 5. The flexible cable or conductor 3 is advantageously connected to the holder 6 and the bus bar 2 through pivotal connections as indicated at 4. The holder 6 is advantageously movable upwardly and downwardly by vertical displacement of the column 7.

Someor all of the conductors 3 of a phase are surrounded by one or more choke elements 10 in accordance with the invention. The choke elements have dimensions which resemble well known insulating elements 11 and they are interchangeable therewith.

The furnace is operated by providing a number of chokes 10 figured from a rough calculation. After the furnace operates for a time, one determines by measurement which phases and which conductors are loaded too high. The choke elements 10 are applied over the conductors 3 in a suitable number by use of connecting conductors 13, 13 and bolts 13a, 13a (not shown in FIG. 1) until the desired operating state is established. With such an arrangement the choke elements 10 are not fixed by previous calculations once and for all but can be adapted to the actually existing conditions. Even if during the operation changes should be discovered or should be desirable, extensive adaptations of these conditions are possible by the addition or removal of choke elements 10. This is advantageously done by the exchange of the choke elements 10 for the insulating elements 11.

The suspension of the choke elements may be effected by special cables, for example by a cable pair 13, 13 of FIGS. 2 and 3 which run along the side of the conductors and to which the elements are clamped by the cable bolt elemetns 13a, 13a. On the other hand, the cable sections may be such (e.g. interengageable) that they may be connected together to form a kind of a cable chain. Alternatively, the individual separately suspended choke elements can be interconnected by straps, pull rods or the ductors sufficient space 20 remains for the passing of the cooling medium which may be liquid or gaseous. The cooling medium is supplied to the hose 15 in a known manner by cable couplings or clips. In FIG. 3 it is shown that the sheets forming the coil may lie one on the other, both in circumferential directions and with respect to a transverse axis, or extend parallel to the longitudinal axis as indicated in FIG. 2.

In the FIG. 4 embodiment, spacer rings 12 are advantageously placed between the sets of coil rings forming the choke core in such a manner that they do not hinder the mobility of the hose 15. For this purpose, the spacer rings may be provided with crown contact surfaces or they may be provided with individual contact cams.

It may be advantageous to apply the above described choke elements not only on the flexible lines, but also on fixed lines, that is, for example, on the section 2 between the transformer and the flexible line 3 or on the supporting arm 6 between the flexible line and the electrodes 5.

While specific embodiments of the invention have been shown and described in detail to illustrate the application of the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles.

What is claimed is:

1. An electric arc furnace comprising, in combination, movable electrodes; current conductors connecting the electrodes to a source of current and each including a flexible portion; iron core choke means surrounding at least the flexible portions of the conductors to adjust the respective inductances to equalize the respective currents in the conductors; and insulation surrounding at the flexible portions of the conductors; plural individual choke elements constituting said choke means, and each comprising an annular iron core surrounding a conductor; the choke elements on each conductor being arranged in closely spaced axially successive relation along the associated conductor, and the number of choke elements on each conductor being selected in accordance with the desired adjustment of the respective inductance of the associated conductor.

2. In an electric arc furnace having movable electrodes, the improvement claimed in claim 1, including individual insulation elements constituting said insulaton; said choke elements replacing a corresponding number of said insulation elements.

3. In an electric arc furnace having movable electrodes, the improvement claimed in claim 2, in which the respective external dimensions of said insulation elements are equal to the corresponding respective external dimensions of said choke elements.

4. In an electric arc furnace having movable electrodes, the improvement claimed in claim 1, in which each an nular iron core comprises plural arcuate sections movable relative to each other, whereby said annular iron cores may be readily placed around a conductor and removed from the conductor.

5. In an electric arc furnace having movable electrodes, the improvement claimed in claim 1, in which the inner peripheries of said annular iron cores are spaced from the external peripheries of the associated conductors to provide annular passageways for flow of coolant around and along the associated conductors.

6. In an electric arc furnace having movable electrodes, the improvement claimed in claim 5, including a respective flexible conduit peripherally embracing the choke elements on each conductor and extending along said choke elements.

7. In an electric arc furnace having movable elec trodes, the improvement claimed in claim 6, including annular spacers interposed between axially adjacent choke elements on each conductor.

8. In an electric arc furnace having movable electrodes, the improvement claimed in claim 1, in which said an- 3,414,656 5 6 nular iron cores consist of ferritic material having a low OTHER REFERENCES loss at adequate permeability.

Welding Handbook, 1942 Ed., American Welding References Cited Society, New York, N.Y., pp. 132-134. UNITED STATES PATENTS 5 BERNARD A. GILHEANY, Primary Examiner. 2,902,524 9/1959 Paxton 13--6 3,255,404 6/1966 Kidwen 323 50 H. B. GILSON, Assistant Examiner. 

